Hi, Josh,
Thank you for your reply. :)
I had allready tested json_encode($query) (as described in the post in partner area, because I may have posted this one wrong...), and now I've also tried your suggestion with variant_id, but I get this: {"errors":{"order":"Required parameter missing or invalid"}}
PS! Variant ID for products, is that Product --> Variants --> Product ID according to the API?
And, yes, I'm using that library - initially I made my own code, but went for this one after a tip and to verify where the error was... :)